During open heart surgery, the heart muscle or myocardium requires vital oxygen and energy supplements during the surgical procedure to prevent deterioration of the myocardium. In order for the surgeon to work on the heart, it must be stopped. This is accomplished by means of a cardioplegic solution or crystalloid which contains potassium chloride (KCL) in an aqueous solution which interferes with the electrical activity of the myocardium on a cellular level. Crystalloid defines a substance that forms a true solution, in solution diffuses readily through a membrane, and is capable of being crystallized.
In cardiovascular bypass, blood from the vena cava of a patient undergoing coronary surgery is sent to a venous reservoir and is passed through an oxygenator or artificial lung where it is mixed with oxygen. A major portion of this oxygenated blood is filtered and returned to the patient for circulation throughout the body to be returned again and gathered from the vena cava.
In order to initiate cardioplegia, a minor portion of the oxygenated blood is withdrawn from the oxygenator and is then mixed in specific ratios with the potassium chloride cardioplegic solution. The mixture is then passed through a heat exchanger mixing device. Then the mixture is intermittently or continuously perfused to the myocardium, usually via the aortic root or the coronary sinus. In some instances, all blood or all cardioplegic solution is perfused to the heart. Blood and cardioplegic solution that seeps out of the left ventricle and surrounding tissue is collected from the chest or pleural area for reuse. There are several suction devices which collect the blood and other fluids from the pleura. If the blood is of high quality it is sent to the venous reservoir for filtration and oxygenation. If the blood is of good quality but is dilute or is mixed with cardioplegia solution, it is suctioned off to a cell saver which operates like a centrifuge to separate the good quality blood cells from the excess cardioplegic solution for reuse.
There are two main types of cardioplegia: cold cardioplegia and warm cardioplegia, the choice of which is determined by the surgeon depending upon the condition of the patient and the type of surgery.
Cold cardioplegia utilizes a cold (about 4.degree.-12.degree. C.) cardioplegic solution comprised of 100% crystalloid solution or a mixture of cardioplegic solution and blood with hypothermia to reduce the energy required by the heart. The solution or mixture is infused intermittently or continuously throughout the cardiac surgery.
Warm cardioplegia utilizes a mixture of oxygenated blood and a cardioplegic solution at a temperature of about 20.degree.-37.degree. C. The mixture is infused continuously or intermittently throughout the cardiac surgery.
Using cold or warm cardioplegia, the mixture of the blood and the cardioplegic solution is carefully controlled. Normally, there is a 4 to 1 ratio of blood to cardioplegic solution although ratios of 1 to 1, 2 to 1, and 9 to 1 ratio are sometimes used. The ratio can be controlled by the diameter of the tubing used to carry the blood (typically 1/4 inch diameter tubing) and the diameter of the tubing used to carry the cardioplegic solution (typically 1/8 inch diameter tubing). The maximum ratio of blood to cardioplegic solution is then partially fixed by the diameter of the tubing.
The fixed ratio of the blood to the cardioplegic solution maintains a constant amount of potassium given to the heart. This can result in potassium overloading which is thought to cause damage to the myocardium. In order to overcome this problem, two or more separate bags of cardioplegic solution can be used which contain different concentrations of potassium. One bag having a high concentration of potassium is used to arrest the heart and the other bag containing a lesser concentration of potassium is used to maintain the heart.
The two or more separate sources or bags of cardioplegic solution are connected to a Y fitting. A clamping means permits the selection of one or the other bag of cardioplegic solution for mixture with blood.
The two respective tubing lines containing the cardioplegic solution and the blood are passed in parallel through a pump such as a roller pump. The two respective tubing lines then pass through a mixing device having a single exit line. The pump delivers the mixture at a specific preset flow rate to the antegrade/retrograde valve of the invention for infusion to the heart.
Infusion is normally conducted at a relatively high flow rate to the aortic root (antegrade infusion) to arrest the heart. Alternate infusion is made at a lower flow rate to the coronary sinus (retrograde infusion) and to the aortic root thereafter.
Cardioplegic solution consists of aqueous solutions of potassium chloride and often contains additional ingredients such as dextrose, glutamate, aspartate, and various other electrolytes such as Ca.sup.+2 and Mg.sup.+2. Cardioplegic solutions are delivered by alternating between antegrade cardioplegia and retrograde cardioplegia containing high and low potassium concentrations.
In order to arrest the heart and to limit the total cardioplegia volume, typically antegrade cardioplegia is given first to the aortic root to supply approximately 20 mEq/L of potassium given at 300-350 ml/min for 2 minutes to stop the heart. Thereafter, retrograde cardioplegia is delivered to the coronary sinus at 100-200 ml/min to supply approximately 10 mEq/L of potassium for about 2 minutes. In this instance, the concentration of potassium is controlled through the flow rate.
Alternately, the high concentration potassium chloride cardioplegic solution can be infused antegrade to arrest the heart. Then, the low potassium cardioplegic solution can be infused to deliver the balance of the potassium.
Thereafter, reinfusions during surgery are divided between 1 minute antegrade and 1 minute retrograde at approximately 20 minute intervals. Reinfusions can also be delivered continuously.
Warm reinfusion is often given prior to restarting the heart. For example, warm reinfusion is delivered at 150 ml/min for 3-5 minutes which is divided between antegrade and retrograde to limit reinfusion injury. Other combinations of cold and warm cardioplegia are utilized depending upon the individual surgeon and the condition of the patient. This invention should not be limited by the various combinations of delivery of cardioplegia used.
Antegrade pressure at the aortic root should be maintained at less than about 300 mm Hg pressure and retrograde pressure at the coronary sinus should be maintained at less than about 50 mm Hg pressure to avoid myocardial edema and hemorrhage. The significant pressure differential requires accurate pressure reading and control. In addition, it is necessary to ensure that the proper pressure is delivered to the aortic root or to the coronary sinus to avoid damage to the heart. Pressure can be controlled by adjustment of the flow rate of the pump. Similarly, the temperature must be monitored and controlled.
Since the antegrade cardioplegic solution and the retrograde cardioplegic solution are introduced into different parts of the heart at different times, two lines or tubes are required. The two lines are connected to a roller or other type of pump. One of the lines must be clamped or otherwise restricted while the other is in operation.
One device which has been used in the past to stop the flow in one line while permitting flow in the other line is in the form of a three way stopcock which selectively permits flow through one or both lines depending on its position.
The three way stopcock device requires two hands for operation making it inconvenient to operate. The stopcock is connected to PVC tubing which gives good visibility but kinking and leaks of the tubing have been experienced. Also, there is possible pressurization of the coronary sinus via communication with the antegrade pressure monitoring line.
Another device utilizes a rotary compression switch and silicone rubber delivery lines. Both lines pass through a housing, one on either side of a circular rotation member which selectively compresses or releases one or both lines depending upon the position of rotation. Thus, both lines can be unclamped in order to prime the lines, and then one line clamped to permit selective flow in the other line, or both lines can be clamped to prevent flow through either line.
There are several disadvantages to the use of the rotary clamping switch. One disadvantage is that two hands must be used to change the position of the switch.
In addition, the network of delivery and pressure lines are easily tangled causing confusion. Moreover, the silicone rubber tubing offers poor visibility for priming.
The above disadvantages are eliminated by the system, valve, and method of the invention.
Thus, it is an object of the invention to provide an antegrade/retrograde method, valve and system which utilizes large bore 1/8" clear PVC tubing with large bore 1/8" Luer connectors. Coextruded PVC tubing is easy to handle reducing tangling and confusion during use. The clarity of the tubing offers good visibility for priming and other visual monitoring of the tubing adding to the safety during use. If desired, color coding can be added for further convenience.
It is another object of the invention to provide an antegrade/retrograde cardioplegia method, system, and valve which facilitates pressure monitoring by a method and valve having two large bore stopcocks. Separate antegrade and retrograde pressure lines provide simultaneous antegrade/retrograde pressure monitoring. Connectors are provided for measurement of aortic root and coronary sinus pressures.
It is another object of the invention to provide an antegrade/retrograde cardioplegia method and system which combines large bore tubing and connectors to reduce pressure drop and blood hemolysis (dissolution or breakdown of red corpuscles with liberation of their hemoglobin). The ergonomically designed valve can be operated with one hand to deliver cardioplegic solution to the aortic root via antegrade flow or to the coronary sinus via retrograde flow. This feature eliminates the need to anchor the valve to the table. Also, the ergonomic design of the valve provides a natural fit to the hand which allows stability when used in different positions and allows for flexible control and movement in the surgical field.